The present invention relates generally to the tracking of magnetic source objects, and more particularly, to a data processing algorithm that permits kinematic tracking in real time of one or more magnetized objects, using a series of magnetic field strength measurements, vector components or total field, collected from one or more magnetometers.
Numerous opportunities exist for sensor systems that can track objects which generate magnetic fields. All types of land vehicles, ships, and aircraft have structural and power systems capable of generating substantial magnetic signatures. Even small inert objects such as firearms and hard tools may exhibit sufficient magnetization to be observed from a distance. Over the past several years, the assignee of the present invention has developed various types of magnetic sensor data processing algorithms and systems capable of localizing, quantifying, and classifying such objects based on their magnetostatic fields. The present invention extends this capability to real time tracking in a way that greatly simplifies solution of the nonlinear field equations.
A magnetostatic field may be generated by any combination of three physical phenomena: permanent or remanent magnetization, magnetostatic induction, and electromagnetic induction. The first occurs in objects that contain metals of the ferromagnetic group, which includes iron, nickel, cobalt, and their alloys. These may be permanently magnetized either through manufacture or use. Second, the Earth's magnetostatic field may induce a secondary field in ferromagnetic structures and also paramagnetic structures if the mass and shape sufficiently enhance the susceptibility. Third, the object may comprise a large direct current loop that induces its own magnetic field. This is often the case with land vehicles that use the vehicle chassis as a ground return.
Tracking objects by sensing and data processing their magnetostatic fields offers several advantages over other methods. One is that the process is passive rather than active. This eliminates potential health and safety hazards that could be associated with some types of active sensor systems, such as those which use various types of electromagnetic radiation. A passive system also permits covert observation, useful to military and intelligence operations as well as law enforcement. Another advantage is that the field is mostly unaffected by natural boundaries, such as space above and the sea or land surface below. It is also unaffected by many adverse environmental conditions such as wind, fog, thunderstorms, and temperature extremes. Yet another advantage is that the magnetostatic field of the tracked object is difficult to conceal or countermeasure, and is therefore useful against hostile subjects.